All the power in the world and not enough battery!

Discussion in 'Amateur Radio News' started by VK6FLAB, Mar 2, 2019.

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  1. KF5LJW

    KF5LJW Ham Member QRZ Page

    That is not a solution, that is an abortion. You are wasting a lot of power being burned up for nothing. The real solution is to use the right battery to begin with. LiFePO4 aka LFP are the only lithium batteries that can be used as drop in replacements for Pb batteries. They use the exact same charge voltages as Pb. Not to mention a lot less expensive than your abortion. Sure hope no one takes your advice, it is dangerous and a waste of money and energy.
     
  2. NL7W

    NL7W Premium Subscriber QRZ Page

    Do you ever say anything nice or positive, or are you always an Amp-Hour (AH)? Good grief.
     
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  3. VK5SA

    VK5SA XML Subscriber QRZ Page

    An Australian "F" call (Foundation licence) is limited to 10W.

    Just sayin.......
     
  4. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    If I may add one tiny correction to Onno's article: if you have a battery of 26AH and load it with 26A, it won't last an hour. Battery capacity is usually stated at 1/20C or in human language: a current draw which is 1/20 of its capacity. So this 26AH battery will give you 20 hours of life at a load of 1.3A. Increase that load and you'll run shorter than the math would have promised you.
     
    K8XG, K3KIC and US7IGN like this.
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    That is Peukert Law.
     
  6. ZS6BV

    ZS6BV Ham Member QRZ Page

    I have used LiFePO4 batteries as well and I end up with flat batteries while operating. The 4S LiPo's give me much better life and are smaller and lighter. A display / warning buzzer monitors the overall voltage and individual cell voltages. I take the in line rectifier out once battery voltage is safe for my radio. While operating the heat sink stays cold.
    It works well for me, so Derek can take his snide comments and place them strategically...
     
    K4FX and WN1MB like this.
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Well I give you credit for admitting you do not know what you are talking about or doing. Of course LeFePO4 is flat, that is what makes them so appealing and useful. At full charge in 4S the voltage is 14.2 and exhausted at 12 volts which is perfect for 12 volt equipment. You get to use all the energy and not waste any as waste heat. Pb on the other hand is a bit steeper of 14.2 down to 10.5 volts. 4S LiPo has a very steep charge/discharge curve of 16.8 volts at full charge, down to 10 volts exhausted.

    That forces you to use some method to bleed off voltage. You say two diodes which will work which means you have to burn off as waste heat of roughly 15% of your battery capacity is burned off as waste heat doing nothing. Sure you can keep them cool with a large enough heat sink which adds weight, takes up space, and rund cost up. LiPo's only have 100 to 200 cycles vs about 1000 for LiFePO4. Everything you gained from using LiPos is wasted and thrown away by hacking it. Sure it can work, just a piss poor way of doing it adding eggs to an already fragile basket.

    Fine for an emergency to SOS, but not a good choice or practice on a permanent station. With LiFePO4 you have access to all the battery capacity from 14.4 down to 12 volts. With LiPo's you can only access a fraction of the battery capacity. You have to burn off 15% of the energy using diodes, and cannot access the energy below 12 volts.

    Now what could be done but complicated is to use a switch mode DC to DC Converter. Those are on the order 95% efficient and would allow you to utilize all th energy capacity. But again that is a band-aid for using the wrong battery type, adding expense, weight, space, and another egg in the basket.
     
  8. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    The guy on the link below uses LiPO4 without problems on his FT-897. Yes, the full-charge voltage exceeds the 13.8V+/-15% slightly but that seems to be no problem at all. In fact, most transceivers only apply the 13.8V directly to the PA transistors, which are rated for 17V in an FT-897. The remaining circuitry is behind voltage regulators. And of course, the moment you start transmitting, the voltage will definitely drop to a level that's within specs.
    https://uuki.kapsi.fi/fnb78li.html
     
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  9. WN1MB

    WN1MB Ham Member QRZ Page

    WA2LXB, WA1ZMS and AC0GT like this.
  10. WD4DUI

    WD4DUI Ham Member QRZ Page

    I want hydrogen fuel cells!

    BTW, please explain why it is detrimental to batteries when connected in parallel for a prolonged time without some sort of battery isolation. I have tried to explain the reason to some people with limited success. They cannot understand why their lead acid batteries fail unexpectedly when not being charged.
    And still the myth of leaving batteries on a concrete floor will kill them persists.
    I know, apples and doughnuts comments in this comment
     

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